The Arctic’s thick cloak of winter sea ice shrank abruptly in the past two years, and some scientists say that means significant changes are in store for northern ice, hungry polar bears and world climate.

“We haven’t seen this before,” said Mark Serreze, a sea-ice expert at the University of Colorado’s National Snow and Ice Data Center, NSIDC. “If the ice losses aren’t restricted to the summer, then this loss is on a slippery slope.”

National Aeronautics and Space Administration and CU researchers published new sea-ice data on the NSIDC website Wednesday, and other results appeared in September issues of Arctic and Geophysical Research Letters.

Sea ice forms and melts over the Arctic Ocean every year as winter turns to summer.

The expanse of water covered by summertime ice has been shrinking steadily for three decades, Serreze said.

The decline, however, has been precipitous in the past five years, with the new melt area measuring an area about twice the size of Texas.

Winter ice held fairly steady until an abrupt decline in 2005 of about 280,000 square miles, or an area the size of Texas, according to the new reports.

If trends continue, the Arctic Ocean’s summertime ice pack could vanish by the end of the century, Serreze said.

“Have we gotten to a tipping point yet? Maybe not quite,” he said, “but in my opinion, we’re getting pretty close.”

The reach of sea ice has both economic and biological impacts, said Josefino Comiso, a research scientist with NASA Goddard Space Flight Center in Greenbelt, Md.

“With less ice, economically, it would be a lot cheaper to transport goods from China and Japan to New York,” Comiso said. “But these regions, they’re actually the most fertile ground for fisheries, and they’re productive because they’re cold.”

Polar bears already appear to be reacting to retreating sea ice, said Claire Parkinson, also a researcher at NASA Goddard.

“They eat, they hunt from the sea ice,” Parkinson said. “When the sea ice retreats, they have to go elsewhere, so they have to go on the land.”

In the Canadian Arctic, polar bears have been wreaking havoc in towns, eating garbage and scaring people, she said.

The Hudson Bay population of polar bears has dwindled from about 1,200 animals in 1989 to about 950 in 2004, Parkinson said, and they’re getting thinner.

Parkinson and her colleagues blamed human-caused global warming for the Arctic changes.

Computer climate models predict Arctic sea-ice melt, and the losses seen in the past two years are very close to those predicted by the models.

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